Hey, I had an idea wherein you could go back to recently posted messages (say, within the past 5-30 minutes) and edit them to fix typos/grammar mistakes/retcon something (with permission from the GM, of course) whilest still keeping a comprehensive log without having to remember 'oh right, he actually meant x' or 'oh right, we retconned that to y'.
Something similar to what Skype offers, I suppose.
Though I'm not entirely sure it would be easily doable given how roll20 is being facilitated in completely online use, I'd certainly hope to hear it would be possible. If not, it can be dealt with easily enough. But the niceties in life are well, nice.